Apparatus for curing resist

ABSTRACT

A resist curing device including a workpiece stage with a plate adapted to support a silicon wafer laid thereupon, a workpiece retention device that vacuum adsorbs the silicon wafer laid upon the plate, a light source unit that provides ultraviolet irradiation to cure resist applied to the silicon wafer, and a workpiece temperature control device that heats and/or cools the silicon wafer supported on the plate, where the plate has an expansion coefficient substantially similar to that of the silicon wafer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a resist curing device in which a resistapplied to a silicon wafer is irradiated with light containingultraviolet rays in the process of semiconductor integrated circuitmanufacture.

2. Description of Related Art

In the production of semiconductor integrated circuits, silicon wafersare subjected to patterning, and a resist comprising photosensitivematerial and base polymer of novolak resin is uniformly applied to thesurface of a silicon wafer as pretreatment to form various types ofcircuits. Photoresists are cured by irradiating silicon wafers withultraviolet rays while heating the silicon wafer to enhance the heatresistance, chemical resistance and dry-etching resistance of resists.

First, a device such as a silicon wafer is held by vacuum adsorption asa workpiece on the surface of a workpiece stage that is provided with atemperature control means and a workpiece retention means for use incuring of such resists. The workpiece is vacuum adsorbed to uniformlyand efficiently transmit heat from the workpiece stage to the workpiecewhile accurately controlling the temperature. The temperature of thesilicon wafer is gradually raised from 100° C. to 200° C. whileirradiating a resist applied to a silicon wafer with light containingultraviolet rays from an ultraviolet lamp. The temperature is thenlowered back to 100° C. following ultraviolet irradiation.

Outstanding resist layer characteristics in terms of heat resistance,chemical resistance and dry-etching resistance is obtained by so doing.For example, the heat resistance temperature of a resist whose heatresistance temperature is 140° C. can be raised to 250° C. by curingwith ultraviolet irradiation.

In this manner, a silicon wafer workpiece is vacuum adsorbed on aworkpiece stage to accurately control the temperature of the waferduring ultraviolet irradiation. However, the diameter of silicon wafersis large, ranging from 150 mm to 200 mm, and there are cases, dependingon the conditions such as the type of resist or the layer thickness, inwhich such a large silicon wafer must be processed at a rapid heatingrate of 1° C./second or more. Accordingly, a workpiece stage is formedfrom metal having good thermal conductivity such as copper to uniformlyheat the entire broad surface of a silicon wafer while raising thetemperature rapidly. Thus, a great difference in linear expansioncoefficients exists between a silicon wafer comprising a single crystalof silicon whose linear expansion coefficient at 20° C. to 300° C. is2.5×10⁻⁶/K and a workpiece stage of copper whose linear expansioncoefficient is 0.334/K.

Accordingly, when a silicon wafer is subjected to rapid rise and drop intemperature while vacuum adsorbed to a workpiece stage, the siliconwafer and workpiece stage rub together due to the great differences inthe amount of linear expansion and the amount of heat shrinkage betweenthe two, thereby creating radial rubbing blemishes on the backside ofthe silicon wafer.

Furthermore, the surface of a workpiece stage may be coated with ceramicto prevent direct contact between a silicon wafer and a metal workpiecestage in consideration of metal contamination of a silicon wafer. Buteven if the surface of a ceramic coating layer is adequately polished,it would remain rough compared to the surface of metal and many rubbingblemishes would form on the backside of the silicon wafer. The number ofsuch rubbing blemishes could amount to 5000 to 15,000 depending onconditions, and their length could extend to the edges of a siliconwafer, reaching 0.5 mm.

The dislocation of the silicon single crystal could develop in thecourse of heating in subsequent steps if such rubbing blemishes developon the backside of silicon wafers, and sleeves could develop in siliconwafers as such dislocations grow, resulting in production rejects.Furthermore, dust of shaved silicon powder that is created when suchrubbing blemishes develop sticks to the backside of silicon wafers andis fed to the subsequent steps. For this reason, the wash in thesubsequent washing process as well as the etching liquid in the etchingprocess become contaminated with dust which is a cause of productionrejects.

Thus, the primary purpose of the present invention is to provide aresist curing device in which rubbing blemishes do not develop on thebackside of a silicon wafer even when a silicon wafer coated with aresist is vacuum adsorbed onto a workpiece stage and is subjected tocuring processing by ultraviolet irradiation while being heated andcooled.

SUMMARY THE OF INVENTION

To attain such purposes, the present invention provides a resist curingdevice with a workpiece stage comprising a light source unit thatcarries out ultraviolet irradiation, a workpiece retention means thatvacuum adsorbs a silicon wafer laid thereupon as a workpiece, and aworkpiece temperature control means that heats and cools the workpiece,wherein the resist applied to the workpiece is subjected to ultravioletirradiation and cured while the workpiece that is held on the surface ofthe workpiece stage is heated, the resist curing device furtherincluding a plate composed preferably of Si (silicon), SiO₂ (quartz),SiC (silicon carbide), or Si₃N₄ (silicon nitride) with through-holes topermit vacuum adsorption from the workpiece stage to act on theworkpiece. The plate is interposed between the workpiece and the uppersurface of the workpiece stage, and ultraviolet irradiation is carriedout while the plate and workpiece are vacuum adsorbed on the workpiecestage by the workpiece retention means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of the present invention.

FIG. 2 is a top planar view of the plate in accordance with the presentinvention.

FIG. 3(A) shows a schematic view of the present invention of FIG. 1being used in a step of the curing process.

FIG. 3(B) shows a schematic view of the present invention of FIG. 1being used in another step of the curing process.

FIG. 3(C) shows a schematic view of the present invention of FIG. 1being used in yet another step of the curing process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention is explained belowbased on the diagrams. FIG. 1 is a schematic cross-sectional viewshowing the resist curing device in accordance with one embodiment ofthe present invention. In FIG. 1, workpiece stage 10 which may be madeof copper has good thermal conductivity. Second adsorption groove 12 isfor vacuum adsorption of plate 60 discussed below that is laid on theupper surface of workpiece stage 10, while the first adsorption groove11 is for vacuum adsorption of a device that constitutes the workpiecethat is laid on plate 60, both the first adsorption groove 11 and thesecond adsorption groove 12 being formed on the upper surface of theworkpiece stage 10. First adsorption groove 11 is connected to firstvacuum pipe 31 while the second adsorption groove 12 is connected tosecond vacuum pipe 32. The first vacuum pipe 31 is connected to adepressurization device (not illustrated) via first electromagneticvalve 33, and the second vacuum pipe 32 is connected to a decompressiondevice via second electromagnetic valve 34. Accordingly, plate 60 isvacuum adsorbed on the upper surface of workpiece stage 10 throughactuation of second electromagnetic valve 34 while the workpiece isvacuum adsorbed on the upper surface of workpiece stage 10 via plate 60through the actuation of first electromagnetic valve 33. The workpieceretention means may include these adsorption grooves 11, 12, vacuumpipes 31, 32, electromagnetic valves 33, 34, and the depressurizationdevices.

Heating means 21 may include a heater and cooling means 22 withwater-cooling pipes through which cooling water circulates are disposedwithin workpiece stage 10. A signal from a sensor (not illustrated) thatdetects the workpiece temperature is input to controller 23, and heatingmeans 21 as well as cooling means 22 are controlled by controller 23based on this signal. The workpiece temperature control means mayinclude heating/ cooling means 21, 22 as well as controller 23.

A plurality of transfer pins 41 that rise and fall through the workpiecestage in the vertical direction, for example, four pins, are disposedwithin workpiece stage 10. The lower edges of transfer pins 41 are heldby ascending/descending plate 42, and transfer pins 41 completeascent/descent actuation by actuator 43.

A light source unit may include ultraviolet lamp 51 and mirror 52surrounding ultraviolet lamp 51 that is disposed on top of workpiecestage 10. Ultraviolet lamp 51 may be a high pressure mercury lamp havingrated consumed power of 8 kW. The light containing ultraviolet rays thatis radiated from ultraviolet lamp 51 is reflected off mirror 52 andirradiated onto a workpiece that is held on the upper surface ofworkpiece stage 10.

Plate 60 may be a thin round plate about 0.675 mm thick with arc-shapedthrough-holes 61 formed in concentric circles, as shown in FIG. 2.Through-holes 61 are aligned with first adsorption groove 11 formed onthe upper surface of workpiece stage 10 when plate 60 is laid on theupper surface of workpiece stage 10. Accordingly, vacuum generated by adecompression device acts on the workpiece via first adsorption groove11 and through-hole 61 to vacuum adsorb the workpiece on the uppersurface of workpiece stage 10 via plate 60.

Four pin holes 62 aligned with the ascent/descent positions of transferpins 41 are opened in plate 60. Accordingly, the workpiece on plate 60can be raised/lowered by transfer pins 41 protruding from the uppersurface of workpiece stage 10.

In accordance with one embodiment of the present invention, plate 60 maybe composed of Si (silicon) which has the same linear expansioncoefficient as that of silicon wafers made of single crystals ofsilicon, or from material whose linear expansion coefficient is similar,including SiO₂ (quartz), SiC (silicon carbide), and Si₃N₄ (siliconnitride).

The respective linear expansion coefficients at 20° C. to 300° C. are asfollows.

Si 2.5×10⁻⁶/K

SiO₂ 0.5×10⁻⁶/K

SiC 4.3×10⁻⁶/K

Si₃N₄ 3.4×10⁻⁶/K

The method of operating the resist curing device pursuant to the presentinvention is explained below based on FIGS. 3(A) to 3(C). First,workpiece W, a silicon wafer whose upper surface is coated with aresist, is held by chuck finger 70, as shown in FIG. 3 (A). Chuck finger70 is moved forward to shift workpiece W to a predetermined positionover workpiece stage 10. At this time, second electromagnetic valve 34shown in FIG. 1 is actuated and plate 60 is vacuum adsorbed at apredetermined position on the upper surface of workpiece stage 10.

Next, transfer pins 41 are raised, workpiece W is received from chuckfinger 70, and chuck finger 70 is retracted to its original position, asshown in FIG. 3 (B). Then, transfer pins 41 are lowered to set workpieceW on plate 60, as shown in FIG. 3 (C). Next, vacuum adsorption ofworkpiece W on the upper surface of workpiece stage 10 via plate 60 canbe completed by actuating first electromagnetic valve 33 shown in FIG.1. Specifically, workpiece W is brought into contact with plate 60 whoselinear expansion coefficient is identical with, or similar to that ofthe workpiece W so that direct contact is not made with workpiece stage10 made of copper with a linear expansion coefficient that is verydifferent.

As the workpiece is held at a predetermined position, heating means 21is actuated and the temperature of workpiece W is raised to 100° C., forexample, after which shutter 53 between ultraviolet lamp 51 andworkpiece stage 10 is opened to irradiate the resist applied on theupper surface of workpiece W with light containing ultraviolet rays. Inaddition, the temperature of workpiece W can be raised at apredetermined heating rate from 100° C. to 200° C., for example. Shutter53 is then closed to halt ultraviolet irradiation, cooling means 22 isactuated to lower the temperature of workpiece W to 100° C. and curingprocessing is completed. When curing processing is completed, firstelectromagnetic valve 33 is closed to release vacuum adsorption ofworkpiece W, and transfer pins 41 are raised to lift up workpiece W fromworkpiece stage 10, whereupon it is received by chuck finger 70 and isconveyed to the next process.

In accordance with the present embodiment, workpiece W, plate 60 andworkpiece stage 10 undergo thermal expansion and thermal shrinkage as afunction of their respective linear expansion coefficients in responseto the aforementioned heating and cooling. However, in accordance withthe present invention, the workpiece W does not make contact withworkpiece stage 10 whose thermal expansion and thermal shrinkage differgreatly. Rather, it makes contact only with plate 60 whose thermalexpansion and heat shrinkage are identical or similar. Consequently,rubbing does not develop between workpiece W and plate 60 so that thebackside of workpiece W does not develop radial rubbing blemishes.Accordingly, dust is not generated and the production rejects insubsequent processes attributable to dust can be avoided.

Furthermore, the workpiece W made of a single crystal of silicon doesnot suffer metal contamination since plate 60 in contact with workpieceW, is made of silicon or silicon compounds.

As explained above, the present invention concerns a resist curingdevice with a workpiece stage comprising a workpiece retention meansthat vacuum adsorbs a silicon wafer as a workpiece, and a workpiecetemperature control means that heats and cools the workpiece, along witha plate composed of material having expansion coefficient similar to theworkpiece such as Si, SiO₂, SiC, or Si₃N₄ with through-holes to permitvacuum adsorption from the workpiece stage to act on the workpiece. Thebackside of the workpiece does not develop rubbing blemishes as theresist applied to the workpiece is irradiated from a light source unitby ultraviolet rays while the plate and workpiece are vacuum adsorbed onthe workpiece stage via the workpiece retention means.

As explained above, the present invention can be used as a resist curingdevice to cure resists applied to silicon wafers by irradiating themwith light containing ultraviolet rays in the process of producingsemiconductor integrated circuits.

We claim:
 1. A resist curing device comprising: a workpiece stage havingpin holes and a workpiece transfer pin within each pin hole forascending/descending transport of a silicon wafer; a separate, removableplate placed upon an upper surface of the workpiece stage which iscomposed of a silicon-based material and supports a silicon wafer laidthereon; a workpiece retention device that vacuum adsorbs the siliconwafer laid on the plate; a light source unit that provides ultravioletirradiation to cure a resist applied to the silicon wafer; and aworkpiece temperature control device that at least one of heats andcools the silicon wafer supported on the plate; wherein the plate has anexpansion coefficient substantially similar to that of the silicon waferand further includes through-holes to allow the workpiece retentiondevice to vacuum adsorb the silicon wafer through the plate, and a pinhole in the plate which is aligned with each said pin hole and transferpin in the workpiece stage.
 2. The resist curing device of claim 1,wherein the plate is made of material selected from a group consistingof Si (silicon), SiO₂ (quartz), SiC (silicon carbide), and Si₃N₄(silicon nitride).